This document discusses research investigating Pythiaceous root pathogens associated with decline of Eucalyptus gomphocephala (Tuart) trees in Western Australia. Several key findings are mentioned: 1) A new Phytophthora species was isolated from declining Tuart trees and soil. 2) Application of phosphite improved crown condition of trees, indicating a potential role of Phytophthora. 3) Loss of fine roots and root tip dieback were observed, suggesting infection by a Phytophthora root pathogen. 4) Further research aims to characterize the new Phytophthora species and evaluate its pathogenicity through inoculation trials.

1. Pythiaceous root pathogens
associated with Eucalyptus
gomphocephala decline in
Western Australia

2. Tuart distribution
in main affected
area
Tuart forest
+ Extent of decline:-
1990
2007
(Distribution map )

3. Expression of typical Phytophthora
symptoms

4. Overview of research
Investigations into
potential role of Phytophthora
species in Tuart decline
Stem, lateral and fine
feeder root surveys
for necrosis Phosphite was applied -
to explore if a role of a
Phytophthora was likely
Phytophthora sp. was
Isolated

5. Roots (magnified sections) illustrating:
fine root loss and root tip dieback

6. • Aim: Assess whether Phosphite, Nutrient
and Insecticide injections can improve
tree health
– Phosphite: 25, 50 & 75 g L-1
– Nutrients: Combined (Zn, Fe & Mn), Zn & Fe
MEDICAP®
– Insecticide: Orthene®.

7. Results after 12 and 24 months
60
Phosphite 25g/L a.i
50 and ZINC year after treatment 1
years after treatment 2
40 Phosphite 25g/L a.i
& complete nutrients
Percentage canopy change (Grimes Index)
30
20
10
0
-10
-20
Source: Peter Scott. PhD student. Murdoch University
-30
Control P25 P50 P75 Com Zn Fe P25 P50, P75, P25, Zn P50, Zn P75, Zn P25, P50, P75,
Com Com Com Fe Fe Fe
Treatments

8. Aim: assess the influence of different
phosphite concentrations tree health
Phosphite at 75, 150, 225,
300 & 375 g L-1
Confirm Phosphite uptake
(foliar)
Monitor Phytotoxicity

9. 20
15
Percentage Change in Canopy Condition
Percentage change in Canopy condition
10
5
0
-5
-10
-15
Control
Control 75
p75 150
p150 225
p225 300
p300 375
p375
Phosphite g/Litre
Treatments

10. Phytophthora isolated from 5 of 32 sites sampled
From 4 declining sites and 1 healthy site

11. AY879291 P. inflata
AF266789 P. inflata
Phylogeny and morphology
g2 Phytophthora inflata
92 DQ486661 P. citricola
DQ396420 P. citricola
EF423556 P.citricola
EF418946 P. citricola
EF193216 P. citricola
DQ648135 P. citricola
1 g2 Phytophthora citricola
AB217677 P. citricola
93 VHS 16158 - P.sp. 4
VHS 16168 - P.sp. 4
VHS 16298 - P.sp. 4
VHS 16439 - P.sp. 4
Phytophthora species tuart
98 Phytophthora species tuart
81 Phytophthora species tuart
Phytophthora species tuart
Phytophthora species tuart
VHS 16803 - P.sp. 4
VHS 16870 - P.sp. 4
93 AY946257 P. tropicalis
100 AY207010 P. tropicalis
100 g2 Phytophthora capsici
AF266787 P. capsici
91 g2 Phytophthora citrophthora
100 g2 Phytophthora botryosa
g2 Phytophthora colocasiae

12. Current Work
• Pathogenicity trial (soil inoculation)
• Describe the new species

14. 140
120
Lesion (mm)
100
80
60
40
20
0
Inoculated Tuart Control Tuart Inoculated Jarrah Control Jarrah
Treatment

16. Phytophthora species and role
in tree declines
• Many new Phytophthora species being
linked to tree declines worldwide
• Strict Quarantine critical

18. Conclusion
Loss of fine roots
were identified Phosphite was applied -
improved crown condition A new Phytophthora
species isolated